The Net Effect of Simultaneous Increases in Air Temperature and CO2 Concentration on Plant Biomass Production
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In discussing their findings, the 19 researchers hailing from 8 different countries report that "responses to single factor treatments were rarely additive," and that "in a combined treatment, effects of elevated CO2 often dominated the response, suggesting a larger sensitivity of terrestrial ecosystems to rising CO2 compared to rising temperatures." In addition, they found that "mineral nitrogen availability declined less in the combined treatment than in the CO2-only treatment, possibly due to the warming-induced acceleration of decomposition."
In light of the first of their two major findings, Dieleman et al. conclude that "ecosystem models should ideally be tested against results from multifactor experiments to optimize their model structures." And in light of the second of their major findings, they conclude that "progressive nitrogen limitation (PNL) may not occur as commonly as anticipated from single factor CO2 treatment studies." In fact, they state that "due to the growing intensity and global distribution of atmospheric deposition of reactive nitrogen compounds," as described by Galloway et al. (2004), "more and more extra-tropical ecosystems are shifting from a state of nitrogen (co-) limitation to a state of nitrogen-saturation," citing Aber et al. (1998). And they say that these ecosystems will be "less prone to exhibit PNL with rising atmospheric CO2."
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Larsen, K.S., Andresen, L.C., Beier, C., Jonasson, S., Albert, K.R., Ambus, P., Arndal, M.F., Carter, M.S., Christensen, S., Holmstrup, M., Ibrom, A., Kongstad, J., Van Der Linden, L., Maraldo, K., Michelsen, A., Mikkelsen, T.N., Pilegaard, K., Prieme, A., Ro-Poulsen, H., Schmidt, I.K., Selsted, M.B. and Stvenbak, K. 2011. Reduced N cycling in response to elevated CO2, warming, and drought in a Danish heathland: synthesizing results of the CLIMATE project after two years of treatments. Global Change Biology 17: 1884-1899.
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